EP0038732B1 - Decationized milk, process for treating milk by a cation exchange resin for the manufacture of decationized milk and use of the decationized milk in the manufacture of curdled milk casein for cheeses and lactoserum - Google Patents

Description

• - soit par fermentation lactique du lait, ce qui nécessite l'entreposage de volumes importants de lait pendant toute la durée de la fermentation, qui peut atteindre 12 à 16 heures,
• - soit par acidification du lait par addition d'un acide minéral ou organique fort (acide chlorhydrique, acide sulfurique, acide lactique entre autres), pour abaisser le pH dudit lait au point isoélectrique de la caséine de lait, auquel se produit la coagulation de la caséine contenue dans ce lait, ce qui conduit à une caséine de qualité mais également à un volume important de lactosérum acide et fortement minéralisé, difficile à valoriser en l'état, et nécessitant le plus souvent un traitement supplémentaire de déminéralisation par échange d'ions ou par électrodialyse ; de plus, ce traitement brutal du lait par un acide fort, risque de dénaturer ou de dégrader certains produits de valeur contenus dans le lait à traiter,
• - soit par passage du lait à travers une couche de résine échangeuse de cations sous forme acide pour remplacer les cations contenus dans le lait par des ions hydrogène et précipiter la caséine du lait sur les particules de ladite résine, ce qui conduit à l'obtention d'une caséine de qualité et d'un lactosérum de bonne valeur nutritive, mais la précipitation de la caséine sur les particules de résine provoque très rapidement l'inactivation de ladite résine.

Conventional processes for the production of casein or milk curd for rennet-free cheeses involve the coagulation of the casein contained in milk by lowering the pH of said milk to the isoelectric point of casein which is around pH 4.6:

• - either by lactic fermentation of milk, which requires the storage of large volumes of milk throughout the duration of the fermentation, which can reach 12 to 16 hours,
• - either by acidification of the milk by addition of a strong mineral or organic acid (hydrochloric acid, sulfuric acid, lactic acid among others), to lower the pH of said milk to the isoelectric point of milk casein, at which the coagulation of the casein contained in this milk, which leads to quality casein but also to a large volume of acid and highly mineralized whey, difficult to develop as it stands, and most often requiring additional demineralization treatment by exchange of ions or by electrodialysis; moreover, this brutal treatment of milk with a strong acid, risks denaturing or degrading certain valuable products contained in the milk to be treated,
• - Or by passing the milk through a layer of cation exchange resin in acid form to replace the cations contained in the milk by hydrogen ions and precipitate the casein of the milk on the particles of said resin, which leads to obtaining a quality casein and a whey of good nutritional value, but the precipitation of casein on the resin particles very quickly causes the inactivation of said resin.

• - dans une première étape, on met le lait en contact avec une résine échangeuse de cations pour abaisser le pH du lait jusqu'à une valeur supérieure au point isoélectrique de la caséine du lait, par exemple à un pH non inférieur à 4,7 et notamment compris entre 4,9 et 5, de manière à éviter toute floculation de la caséine du lait susceptible de provoquer l'emprisonnement des grains de résine échangeuse par la caséine floculée ;
• - dans une seconde étape, on acidifie le lait ainsi traité par addition d'un acide dilué jusqu'à l'obtention d'un pH de 4,6, qui est le point isoélectrique de la caséine du lait pour coaguler cette caséine que l'on récupère.

In order to remedy this drawback, according to a recent process described in the European patent application published under the number 0004231, it has been proposed to operate in two stages:

• - in a first step, the milk is brought into contact with a cation exchange resin to lower the pH of the milk to a value greater than the isoelectric point of the milk casein, for example at a pH not less than 4.7 and in particular between 4.9 and 5, so as to avoid any flocculation of the milk casein liable to cause the trapping of the exchange resin grains by the flocculated casein;
• - In a second step, the milk thus treated is acidified by adding a dilute acid until a pH of 4.6 is obtained, which is the isoelectric point of the milk casein to coagulate this casein that l 'we recover.

However, the addition in the second stage of an acid to acidify the milk, in addition to representing a great risk of corrosion for the manufacturing equipment, leads to an acid whey which is still highly mineralized, requiring for its marketing a total demineralization or partial expensive.

Furthermore, according to another proposal described in the French patent application published under No. 2,331,963, the skimmed milk is concentrated by ultrafiltration, to obtain a milk concentrate and a milk ultrafiltrate (or filtration liquid), then the casein of the milk concentrate is precipitated by addition of the ultrafiltrate, the pH of which has been lowered beforehand by cation exchange below the normal value of 4.3-4.8, for example between 1 and 2.5 .

The milk concentrate is a milk enriched with casein and soluble proteins (up to 17-19 g per 100 g of milk concentrate against 3 to 3.2 g per 100 g of normal milk).

The milk ultrafiltrate essentially contains the soluble elements of milk, i.e. lactose, soluble mineral salts (0.45-0.48 g per 100 g of ultrafiltrate), and non-protein nitrogenous substances (0.12 g-0.18 g per 100 g of ultrafiltrate). It is a “whey devoid of protein nitrogenous substances.

Because the milk ultrafiltrate does not contain casein or protein nitrogenous substances, there is no precipitation of these materials on the cation exchange resin particles during the treatment of said ultrafiltrate with the cation exchange resin.

However, the concentration of milk by ultrafiltration requires the implementation of a technique costly in investment and operating costs to obtain a milk concentrate, which can have the composition of the drained cheese and from which cheeses can be prepared. without resorting to the technological stage of drainage.

If, in order to coagulate the casein of the milk concentrate, it was necessary to reintroduce into it a significant quantity of milk ultrafiltrate (which it was difficult to get rid of) after lowering its pH by means of a cation exchange resin, all benefit that could be expected from the concentration by ultrafiltration would be canceled.

In addition, the casein yield relative to the weight of liquids (milk concentrate + milk ultrafiltrate) is unimportant since the volume of liquids used is more than double the volume of the milk concentrate and that only the milk concentrate contains the casein to clot.

However, the inventors have found that by bringing milk into contact with a cation exchange resin in acid form, the pH of the milk could be lowered to the isoelectric point of the milk casein (pH 4.6) or below this isoelectric point without causing the coagulation of the casein contained in this milk, if the milk-exchange resin mixture is kept in a low temperature range of 0 to 4 ° C, while at ordinary temperature or at at moderately high temperatures, coagulation of milk casein takes place as soon as the isoelectric point of casein is reached.

In addition, the inventors have also discovered that by lowering the pH of milk to a pH less than or equal to 3.8, operating in the temperature range from 0 to 4 ° C and using the cation exchange resins under acid form, a decationized milk is obtained, that is to say largely freed from calcium, sodium, potassium cations, having a mineral content less than 4 g / liter, with a Ca / P ratio less than 0 , 5, a pH less than or equal to 3.8, that is to say much lower than the isoelectric point of casein (while the pH of normal milk is 6.7), and containing all the nitrogenous materials normal milk protein and lactose; this decationized, acidulated milk has the particularity of being able to be stored without special precautions for several days at a temperature above 4 ° C, for example at normal temperature (it is therefore not necessary to keep it at 0-4 ° C) without coagulation of the casein it contains, or microbial development.

Likewise, this acidified decationized milk can advantageously be used to acidify normal milk and bring it to the desired pH.

More particularly, it can be used to acidify mildly normal untreated milk and bring the pH of the two milks to the isoelectric point of the milk casein to cause the coagulation of the casein contained in both other milk for the preparation of acid casein or acid curd for rennet-free cheeses, and whey, which represents an appreciable economic advantage since the treatment with cation exchange resin can be limited to a fraction only a batch of milk intended for the manufacture of casein or curd.

The present invention therefore relates to a decationized, acidulated milk, having a Ca / P ratio of less than 0.5, remarkable in that it contains the same contents of proteinaceous matter and lactose as those of ordinary milk, a content of mineral elements less than 4 g / liter and in that it has a pH less than or equal to 3.8.

The present invention also relates to a process for treating milk by means of a cation exchange resin in acid form, with a view to the preparation of an acidified decationized milk, without the addition of strong mineral or organic acid; this process involves contacting the milk with a cation exchange resin in acid form, at a temperature of 0 to 4 ° C, preferably from 0 to 2 ° C, for the time necessary to lower the pH of said milk to a value less than or equal to 3.8, preferably between 1.5 and 3.5, followed by the separation of the acidified decationized milk obtained from the exchange resin.

A contact time of 1 to 10 minutes is generally sufficient for the desired pH to be reached; this contacting time may be further reduced if the milk and the resin are kept under stirring; the volume ratio of the treated milk to the exchange resin is preferably from 5: 1 to 15: 1.

As exchange resins, it is possible to use cation exchange resins in acid form, of the conventional type, used in conventional demineralization, including those used for demineralization of whey.

In particular, it is possible to use, according to the invention, strongly acid cation exchange resins, with a polystyrenic skeleton, carrying sulfonic acid groups, presented in the form of gels or macroporous solids (beads, sticks, etc.).

Macroporous type resins are preferred to gel type resins because of their better mechanical strength.

The highly acidic cationic resins with a polystyrenic backbone containing sulphonic acid groups are sold under the following brands:

• - « Duolite C 26 » ® (copolymère styrène-divinylbenzène à groupements acides sulfoniques ; billes de granulométrie 0,3 à 1,2 mm ; densité apparente 0,85 kg/l).
• - « Amberlite 200. ®et « Amberlite 252 » (copolymère styrène-divinylbenzène à groupements acides sulfoniques ; densité apparente 0,80 kg/I ; granulométrie 0,4-0,5 mm).
• - « Lewatit SP 112 » (polystyrène à groupements acides sulfoniques; billes de granulométrie 0,3-1,5 mm ; densité apparente 0,70-0,80 kg/l).
• - « Kastel C 300 P » ®et « Kastel 300 AGRP (copolymère styrène-divinylbenzène à groupements acides sulfoniques ; billes de granulométrie 0,3-1,2 mm ; densité apparente 0,84-0,86 kg/I).
• - « Dowex MSC-1 » ®(copolymère styrène-divinylbenzène sulfoné ; billes de granulométrie 0,29-0,84 mm ; densité apparente 0,80 kg/1).

The following strongly acidic cationic resins, with macroporous structure are preferred:

• - "Duolite C 26" ® (styrene-divinylbenzene copolymer with sulfonic acid groups; beads with a particle size of 0.3 to 1.2 mm; apparent density 0.85 kg / l).
• - "Amberlite 200. ® and" Amberlite 252 "(styrene-divinylbenzene copolymer with sulphonic acid groups; apparent density 0.80 kg / I; particle size 0.4-0.5 mm).
• - “Lewatit SP 112” (polystyrene with sulphonic acid groups; beads with a particle size of 0.3-1.5 mm; apparent density 0.70-0.80 kg / l).
• - "Kastel C 300 P" ®and "Kastel 300 AGRP (styrene-divinylbenzene copolymer with sulphonic acid groups; beads with particle size 0.3-1.2 mm; apparent density 0.84-0.86 kg / I).
• - “Dowex MSC-1” ® (sulfonated styrene-divinylbenzene copolymer; beads with a particle size of 0.29-0.84 mm; apparent density 0.80 kg / 1).

The treatment of milk with the cation exchange resin can be carried out by techniques known per se, either by percolating the milk through a fixed bed of cation exchange resin, or by passage of the milk against the current with the cation exchange resin, either by mechanical or pneumatic agitation of the milk-cation exchange resin mixture, or by any other suitable method.

After saturation of the cation exchange resin with the milk cations, a regeneration of said exchange resin is carried out with an acid. After rinsing the exchange resin thus regenerated with decationized water, the regenerated exchange resin is ready for a new treatment cycle.

The present invention also relates to the use of decationized acidulated milk according to the invention for the acidification of milk with a view to the preparation of acidified milks, casein, acid curd for rennet-free cheeses, and whey.

For the preparation of acidified milks, the acidified decationized milk is mixed with normal milk until the desired pH is obtained.

For the preparation of milk casein and whey, the acidified decationized milk is mixed with a quantity of normal untreated milk, sufficient to raise the pH of the mixture to the vicinity of the isoelectric point of milk casein, followed by reheating the mixture thus obtained to a temperature of 10 to 60 ° C., in order to coagulate the casein contained both in the treated milk and in the untreated milk and the casein thus coagulated and the whey thus obtained are recovered.

More particularly, the decationized acidulated milk is mixed with a certain volume of normal milk. untreated (preferably a volume equal to that of decationized milk) to raise the pH of the mixture to a pH of 4.4-4.6 and the mixture thus obtained is heated to a temperature of 40 to 50 ° C to cause the coagulation of the casein contained in said mixture.

This coagulated casein is separated from the whey then washed with water, wrung and dried according to traditional methods (spray drying, or by hot air in a fluidized bed) or else resuspended in hot water, preferably at 75 °. C and transformed into alkaline or alkaline earth metal caseinates (sodium, potassium, calcium) or into ammonium caseinate.

The recovered whey (which contains only the cations provided by the untreated milk) can then be dried as it is or after neutralization or else undergo any usual technological operation such as demineralization, ultrafiltration, concentration by reverse osmosis.

The whey obtained according to the process of the present invention has a reduced content of mineral elements, a low content of chlorides compared to whey produced by traditional manufacturing, and the ratios of the following mineral elements:

It is remarkable that this whey concentrated by ultrafiltration or not has good swelling properties and in any case superior to those of a casein whey obtained by direct acidification, as much on the volume after threshing as on the texture.

Furthermore, for the use of acidified decationized milk according to the invention for the preparation of acid curd for rennet-free cheeses, in particular “cottage cheese”, - the decationized acidulated milk is mixed with normal untreated milk in sufficient quantity to raising the pH of the mixture to near the isoelectric point of the milk casein, - the mixture thus obtained is heated to a temperature of 10 to 60 ° C. in order to coagulate in the form of curds the casein contained both in the decationized milk acidulated and in normal untreated milk, - the curd formed is cut, it is subjected to cooking at a temperature between 48 and 60 ° C., the whey is drawn off which is recovered, the curd is washed with cold water then drain it thoroughly.

More particularly, the acidified decationized milk is mixed with normal untreated milk, previously cooled to a temperature of 0 to 4 ° C., in sufficient quantity (preferably a volume equal to that of the decationized milk) to raise the pH of the mixture to a value of 4.4-4.8, preferably 4.4-4.6, then the mixture is warmed to a temperature of 30 to 35 ° C to coagulate the curd.

It is thus possible to produce by the process according to the invention described above, in particular the types of cheese called as follows: "cottage cheese", "queso blanco", "quark", "cheddar-like cheese", "ricotta", “Blue cheese •, and cheese for pizza.

The invention will be described in the following with reference to the attached drawing in which the single figure shows schematically an industrial installation for the implementation of the method according to the invention.

If we refer to this single figure, skim milk is stored in two tanks (1a) and (1b). From one of these tanks, the milk is transported by a pump (2) in one of the two reactors (3a) (3b) via the line (4) after cooling to a temperature below 4 ° C in the heat exchanger (5) with a cryogenic liquid. In the reactor (3a) or (3b), the milk is brought into contact with a strongly acidic cationic resin (6) (in the form of beads) with sufficient stirring provided by agitators (7) to keep the resin beads in suspension in milk. When the pH measured on the pH meter (8) reaches the desired value (generally less than 3.5) the decationized acidulated milk is transferred to the storage container (9) by simple gravity or by air pressure, via line 10; the resin beads are retained in the reactor (3a) or (3b) by a sieve (11) placed at the bottom of the reactor. After rinsing with water admitted in 12a of the milk retained between the resin beads, these are regenerated by a dilute hydrochloric acid solution introduced in 12b, then rinsed with water via a ramp dispersion (12). During this regeneration, the milk is treated on the second reactor.

The acidified decationized milk stored in the tank (9) is mixed in the coagulation head (15) with the untreated milk stored in the tank (1a) or (1b) possibly after cooling in the heat exchanger 5, in proportion such that the pH is between 4.4 and 4.6. The volume of decationized milk is delivered according to the pH setpoint by a variable flow pump (13) slaved to the pH meter (14). Coagulation occurs in the coagulation head (15) by direct injection of steam regulated at 16. After the chambering carried out in (17), the product obtained is recovered. For the preparation of casein, the curd is separated from the whey by a filter (18) placed at the entrance of a first washing tank (19). The whey is collected in 20, for further processing while the curd is washed with water supplied by (21) then discharged through a line (22) to a second washing tower not shown.

The following examples are given to illustrate the implementation of the process of the invention in the installation described above.

Example 1 Preparation of decationized milk.

10 volumes of skimmed milk cooled to 2 ° C are mixed with stirring to one volume of strongly acidic cation exchange resin (form H ⁺ ) marketed under the name “Duolite C 26 ^” (styrene-divinylbenzene copolymer sulfonated, with structure macroporous), presented in the form of beads of 0.3 to 1.2 mm. After five minutes, the milk is separated from the resin which is washed with water and regenerated with a 10% hydrochloric acid solution; the decationized milk thus collected is subjected to analysis and corresponds to the following composition:

Decationized milk is characterized by a greatly reduced content of mineral matter and a pH much lower than the isoelectric point of milk casein (3.2 g / I of mineral matter against 7.9 g / 1 for the starting milk; pH 2.3 against pH 6.7 for the starting milk).

Decationized milk no longer has the white color and opacity of normal milk; it appears as a translucent greenish yellow liquid.

• 10 volumes de lait écrémé non traité sont mélangés au lait décationisé ainsi recueilli. Dès que le pH du mélange a atteint la valeur 4,4 à 4,6, le mélange est réchauffé à 45 °C par injection directe de vapeur pour coaguler la caséine du lait. La caillebotte est séparée du lactosérum par filtration. Après lavage à l'eau, la caillebotte est essorée, puis remise en suspension dans de l'eau à 75 °C et neutralisée par une solution aqueuse de soude à 10 % jusqu'à un pH final de 6,6. La solution de caséinate ainsi obtenue est exempte de toute impureté. Après séchage par atomisation on obtient une poudre blanche de caséinate de sodium, au goût neutre et franc. La caillebotte lavée et le caséinate de sodium sont soumis à l'analyse. ainsi que le lactosérum recueilli.
  

This decationized milk has no visible sediment after 48 hours storage at room temperature. Casein preparation:

• 10 volumes of untreated skim milk are mixed with the decationized milk thus collected. As soon as the pH of the mixture has reached the value 4.4 to 4.6, the mixture is heated to 45 ° C. by direct injection of steam to coagulate the casein of the milk. The curd is separated from the whey by filtration. After washing at water, the curd is drained, then resuspended in water at 75 ° C and neutralized with a 10% aqueous sodium hydroxide solution to a final pH of 6.6. The caseinate solution thus obtained is free from any impurity. After spray drying, a white powder of sodium caseinate is obtained, with a neutral and frank taste. The washed curd and sodium caseinate are subjected to analysis. as well as the collected whey.
  

Example 2 Preparation of decationized milk.

1 volume of cationic resin in H ⁺ form "Duolite C 26" ® (cationic resin with polystyrene skeleton with sulfonic functional groups presented in the form of beads of 0.3 to 1.2 mm), is placed in a double-walled column, thermostatically controlled at 2 ° C; 10 volumes of milk cooled to 2 ° C are decationized by passing against the current, through the resin, at a rate of 5 volumes / hour. Decationized milk is collected. Analysis of this milk gives the following composition:

Decationized milk is characterized by a reduced mineral content (3.5 g / I compared to 8.25 g / I for untreated milk) and by a pH below the isoelectric point of milk casein (pH 2.4 against pH 6.7 for untreated milk).

Casein preparation.

1 volume of decationized milk is mixed with 1 volume of untreated milk. The pH of the mixture is 4.5. This mixture is heated to between 30 and 60 ° C (50 ° C in this example) to agglomerate the casein. The curd is separated from the whey then washed and wrung out.

The use of 10 liters of untreated milk and 10 liters of decationized milk gave 1,600 kg of curd with the following composition; the composition of the whey collected is also given below, as well as the composition of a serum from the traditional manufacture of casein by acidification with hydrochloric acid, given for comparison:

The casein yield at 10% water per 100 liters of milk is 3.1 kg; the yield in liters of milk per kg of casein at 10% water is 32.

The whey obtained has a low mineralization (7.25% of ash against 10.5-12% for hydrochloric serum) with in particular a low content of chlorides (2.9% of chlorides against 7-7.5% for hydrochloric serum).

Example 3 Preparation of decationized milk.

1 volume of cationic resin in H ⁺ form "Duolite C 26" is placed in a double wall column, thermostatically controlled at 2 ° C; 10 volumes of milk cooled to 2 ° C. are decationized by passage, cocurrently, through the resin at a flow rate of 5 volumes / hour. Decationized milk is collected. Analysis of this milk gives the following composition:

This decationized milk is characterized by a reduced content of mineral matter (3.1 g / l against 7.7 g / l for untreated milk) and by a pH below the isoelectric point of milk casein (pH 2.2 against pH 6.7 for untreated milk).

Casein preparation.

1 volume of decationized milk is mixed with a volume of untreated milk to bring the pH of the mixture to 4.4. This mixture is then reheated to 45 ° C for the coagulation of the casein.

The curd is separated from the whey then washed and wrung out.

The collected whey is analyzed and compared to a serum from the traditional manufacture of casein by acidification of milk with hydrochloric acid.

The whey collected is weakly mineralized (7.65% of ash against 10.5-12% for hydrochloric serum) and contains few chloride ions (2.85% of chlorides against 7 to 7.5% for hydrochloric serum ).

Example 4 Preparation of neutralized whey.

The whey obtained in the above examples are neutralized to bring them into a pH zone of between 5.5 and 6.5. The composition of these neutralized sera is given below:

Example 5 Cheese making without rennet. Preparation of decationized milk.

1,000 liters of pasteurized skimmed milk cooled to 2 ° C. are mixed with stirring to 100 liters of strongly acidic cation exchange resin (form H ⁺ ) sold under the name “Duolite C 26” ® (styrene-divinylbenzene sulfonated copolymer , with a macroporous structure) presented in the form of beads from 0.3 to 1.2 mm. After five minutes, the milk is separated from the resin; we wash it with water and it is regenerated with a 10% hydrochloric acid solution; the decationized milk thus collected is subjected to analysis and corresponds to the following composition:

Decationized milk is characterized by a greatly reduced content of mineral matter and a Ph much lower than the isoelectric point of milk casein (3.2 g / I of mineral matter against 7.9 g / I for the starting milk; pH 2.4 against 6.65 for the starting milk.

Decationized milk no longer has the white color and opacity of normal milk; it appears as a translucent greenish yellow liquid.

This decationized milk does not show visible sediment after 48 hours storage at room temperature.

Preparation of the drained sour curd.

1000 liters of pasteurized skimmed milk cooled to 2 ° C are mixed with the decationized milk thus collected.

The pH reaches a value between 4.4 and 4.5. The mixture is slowly reheated to 32 ° C. to obtain the coagulation of the milk protein materials in the form of a curd.

As soon as the curd obtained has a suitable firmness, it is cut. The cut curd is left to stand for about 15 minutes and then it is cooked. The curd is reheated very slowly to a temperature between 52 and 55 ° C and kept for about 1 hour at this temperature, until the curd has the desired firmness.

After drawing off the whey, the curd is washed and cooled with bleach (10 mg / liter of free chlorine) acidified to pH 5.0, then drained; washing and draining operations are repeated several times, ending with ice water (between 4 and 5 ° C).

The curds are again drained thoroughly to remove excess water.

Preparation of cheese.

Drained curds can be packed with or without salt or can be creamed and salted in a manner known per se.

The product obtained has the texture and taste of traditional cheeses like "cottage _cheese.

Composition of the cheese obtained by the process of the invention.

(Siehe Tabelle, Seite 10 f.)

Claims (30)

1. Acidulated decationized milk, with a Ca/P ratio less than 0.5, characterized in that it has the same protein and lactose content as ordinary milk, and a mineral substances content less than 4 g/litre, and a pH less than or equal to 3.8.

2. Process for the treatment of milk using a cation-exchanging resin in acid form for preparing the decationized milk according to claim 1, characterized in that it consists in placing the milk in contact with the cation-exchanging resin in acid form, at a temperature of between 0 and 4°C, for the period necessary to lower the pH of the said milk down to a value below or equal to 3.8, and separating the decationized milk obtained this way from the exchanging resin.

3. Process according to claim 2, characterized in that the milk is placed in contact with the cation-exchanging resin for the period necessary to lower the pH of the said milk to between 1.5 and 3.5.

4. Process according to claim 2 or 3, characterized in that the resin is a strongly acid cation-exchanging resin, with polystyrene skeleton carrying sulfonic acid groups, with a gel or macroporous structure.

5. Process according to claim 2, characterized in that the volume ratio of the treated milk to the exchanging resin is between 5 : 1 and 15 : 1.

6. Process according to claim 2, characterized in that the milk is placed in contact with the cation-exchanging resin at a temperature of between 0 and 2°C.

7. Process according to claim 2, characterized in that the milk to be treated is skim milk.

8. Process according to claim 2, characterized in that the milk is placed in contact with the exchanging resin under stirring or by percolation, or at counter-current.

9. Process for utilizing the decationized milk according to claim 1, to acidify ordinary milk, characterized in that the said acidulated decationized milk is mixed with the ordinary milk to be treated until the required pH is reached.

10. Process for utilizing the decationized milk according to claim 1, for preparing casein and lactoserum, characterized in that it comprises mixing the decationized milk with a quantity of non-treated ordinary milk, sufficient to raise the pH of the mixture to around the isoelectric point of the milk casein, and heating the resulting mixture to a temperature of between 10 and 60 °C, to coagulate the casein contained both in the treated milk and in the non-treated milk, and extracting the coagulated casein and the lactoserum obtained this way.

11. Process according to claim 10, characterized in that the decationized milk is mixed with enough non-treated ordinary milk, to raise the pH of the mixture to between 4.4 and 4.6.

12. Process according to claim 10 or 11, characterized in that the mixture of decationized milk and of non-treated milk is heated to between 40 and 50 °C to coagulate the casein.

13. Process according to claims 10 or 11, characterized in that the volume ratio between the quantity of non-treated milk and that of decationized milk is 1 : 1.

14. Process according to claim 10, characterized in that the extracted casein is washed in water, drained and then dried.

15. Process according to claim 10, characterized in that the extracted casein is washed in water, drained, and replaced in suspension in hot water, at preferably 75 °C and converted into alkaline or alkaline-earth or ammonium caseinate, and then dried.

16. Process according to claim 10, characterized in that the extracted lactoserum is neutralized by an alkaline or alkaline-earth hydroxide, and then concentrated and dried.

17. Milk casein obtained by the process according to any one of claims 10 to 15.

18. Lactoserum obtained by the process according to one of claims 10 to 13 and 16.

19. Lactoserum characterized in that it presents a reduced mineral content, a low chloride content comparatively from the serum obtained from conventional manufacture and the following mineral elements ratios Ca/P < 1 ; K/P < 1.3 and P/CI , 0.6.

20. Process for utilizing the decationized milk according to claim 1, to prepare acid curds for making cheese without rennet, and lactoserum characterized in that it comprises

- mixing the decationized milk with non-treated normal milk, in sufficient quantity to raise the pH of the mixture to around the isoelectric point of the milk casein ;

- heating the resulting mixture to a temperature of between 10 and 60 °C to coagulate into curd the casein contained both in the acidulated decationized milk, and in the non-treated milk, and

- cutting the curd which has formed, and baking it at a temperature of between 48 and 60°C, and extracting the lactoserum, washing the curd in cold water and draining it.

21. Process according to claim 20, characterized in that the non-treated ordinary milk is cooled down beforehand to a temperature of between 0 and 4°C.

22. Process according to claim 20 or 21, characterized in that the decationized milk is mixed with enough non-treated ordinary milk to raise the pH of the mixture to a value of 4.4 to 4.8.

23. Process according to claim 20, 21 or 22, characterized in that the mixture of decationized milk and non-treated milk is heated to a temperature of between 30 and 35 °C to coagulate the curd.

24. Process according to claim 20 or 21, characterized in that the volume ratio between the quantity of non-treated milk and the quantity of decationized milk is 1 : 1.

25. Process according to claim 20 or 21, characterized in that the lactoserum extracted is neutralized by an alkaline or alkaline-earth hydroxide and concentrated and dried.

26. Milk acid curd obtained by the process according to any one of claims 20 to 24.

27. Cheese without rennet prepared from the curd according to claim 26.

28. Lactoserum obtained by the process according to claims 20 to 25.

29. Decationized milk obtained by the process according to any one of claims 2 to 8.

30. Acidified milks obtained by the process according to claim 9.

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